Render *.aspx within an MVC IView.Render() method

Question

I want to render an *.aspx instead of an *.ascx

namespace GenericMVCPlatform.Generics
{
    public class PlatformView : IView
    {
        public void Render(ViewContext viewContext, System.IO.TextWriter writer)
        {
             // Here I would like to render an *.aspx instead of a *.ascx
        }

        private static MvcHtmlString PartialFor<TPlatformView>(this HtmlHelper instance, TPlatformView viewModel)
        {
            // This one only works for *.ascx
            var result = instance.Partial("~/Views/Shared/PlatformView/Index.ascx" , viewModel);
            return result;
        }
    }
}

Earlier I successfully rendered *.ascx using HtmlHelper. But how do I render *.aspx?